"git config --get" used to diagnose presence of multiple definitions of the same variable in the same configuration file as an error, but it now applies the "last one wins" rule used by the internal configuration logic.

Strictly speaking, this may be an API regression but it is expected that nobody will notice it in practice.

Original answer (November 2010)

The git config man page mentions:

The variable names are case-insensitive and only alphanumeric characters and - are allowed.There can be more than one value for a given variable; we say then that variable is multivalued.